Summary
Automatic room upgrade handling can be used maliciously to bridge a room non-consentually
Workarounds
Disabling the automatic room upgrade handling can be done by removing the roomUpgradeOpts key from the Bridge class options.
References
The issue is patched by https://github.com/matrix-org/matrix-appservice-bridge/pull/330
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If you have any questions or comments about this advisory, email us at [email protected].
Impact
If a bridge has room upgrade handling turned on in the configuration (the roomUpgradeOpts key when instantiating a new Bridge instance.), any m.room.tombstone event it encounters will be used to unbridge the current room and bridge into the target room. However, the target room m.room.create event is not checked to verify if the predecessor field contains the previous room. This means that any mailcious admin of a bridged room can repoint the traffic to a different room without the new room being aware.
A critical operation is accessible without requiring any authentication. Typical impact: any user can invoke the privileged function.
CVE-2021-32659 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.6.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Versions 2.6.1 and greater are patched.
Frequently Asked Questions
- What is CVE-2021-32659? CVE-2021-32659 is a medium-severity missing authentication for critical function vulnerability in matrix-appservice-bridge (npm), affecting versions < 2.6.1. It is fixed in 2.6.1. A critical operation is accessible without requiring any authentication.
- How severe is CVE-2021-32659? CVE-2021-32659 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of matrix-appservice-bridge are affected by CVE-2021-32659? matrix-appservice-bridge (npm) versions < 2.6.1 is affected.
- Is there a fix for CVE-2021-32659? Yes. CVE-2021-32659 is fixed in 2.6.1. Upgrade to this version or later.
- Is CVE-2021-32659 exploitable, and should I be worried? Whether CVE-2021-32659 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-32659 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-32659? Upgrade
matrix-appservice-bridgeto 2.6.1 or later.